Question

How do you calculate the atomic mass of magnesium?

Answer 1

Hint : We know that in order to calculate the average atomic mass of magnesium, we should first know that the exactly average atomic mass is. An average atomic mass plays an important role while solving this type of problem. We need to know the basics of the concept to solve this.

Complete Step By Step Answer:
The average atomic mass of an element is the sum of the product of the masses to abundance in nature. Its unit is generally expressed as a $amu$ (Dalton).
Let us first understand what atomic mass is: Atomic mass is said to be mass of atom. The atomic mass which usually is expressed in $u.$ The mass of proton, neutron as well as electron together will give atomic mass. We know that mass of electrons are much lesser as
Compare the mass of the proton as well as the neutron. Therefore the mass of the electron would not influence that much in calculation of an atomic mass of the atom.
The abundance is stated as: We would need to check that percentage values equal $100$ :
$78.99+10.00+11.01=100$
Which they do, and then just use "ratio math":
$\left( 0.7899\times 23.98504 \right)+\left( 0.100\times \text{ }24.98584 \right)+\left( 0.1101\times 25.98259 \right)=24.30505u$
$78.99$ of around $23.98504u$
$10.00$ of around $24.98584u$
$11.01$ of around $25.98259u$
We will check percentage values around equivalent to $100$ :
$78.99~+~10.00~+~11.01~=~100$
Thus by the "ratio math" we get;
$\left( 0.789~\times 23.985 \right)~+~\left( 0.100~\times ~24.985 \right)+\left( 0.110~\times ~25.982 \right)~=~24.305u$
Therefore, Atomic Mass of magnesium is $24.305u$

Note :
Generally the concept of an average atomic mass helps us reach an answer. Since there is no interference of the unit as everything is in the form of percentage but we need to take care while solving problems. We have to remember that the atomic mass and molar mass are not the same.
-Atomic mass is applicable only for atoms.
-But molar mass is applicable to anything that can present in a mole.